could be your ignition modual
According to my Chilton's Auto Repair Manual : The 225 slant six cylinder engine in a 1978 Dodge has spark plugs gapped at : ( .035 inch )
( .035 inch ) spark plug gap for a 1973 Dodge 318 V8 engine , according to my Chilton book
My Chilton repair manual shows : On a Dodge 440 V8 engine , # 1 on the distributor cap faces to the front and slightly towards the passenger side
The factory shop and repair manual if they will sell you one. Then I prefer the Chilton brand Then Haynes All will do for basic things like torque specs and spark plug gaps.
get a Chilton's Manual from a local auto parts store...
Chilton's repair manual says its .054 in. for the gap setting
.044" per the Chilton manual, Napa Auto website and the sticker in the engine compartment.
( .040 inch ) according to my Chilton repair manual for the 350 - 2 barrel
My Chilton's says 48 to 53 thousandths dpf If it is a Grand Caravan 3.8L V6, then the gap is .050
.050 inch according to motorcraft.com but my Chilton repair manual shows .044 inch
The spark plug gap for a 1994 Ford Explorer with the 4.0 L OHV motor is .052 to .056 range - Chilton repair manual shows .054
look in the owners manual for that info.